how much +healing does a holly/disc priest need to start heroics?
and how much + healing does he need to be able do all heroics comfortably?

ty

oh yea, and how much hp/mana is good enough

oh yeah, and how much hp/mana is required? :D

This is a difficult question to answer, because it's not a black and white answer.  First of all, not all heroics are created equal, some (like Slave Pens, Underbog, Botanica, etc) are fairly easy, even without a perfect group, while some (Shattered Halls, Magister's Terrace, etc.) can be difficult even with a well geared, well balanced group.

That said, assuming you're going for some of the easier ones, and you have a good group that's equally geared, a priest can probably pull it off at around 1100-1200 Healing, but that would probably involve a couple wipes even in some of the easier ones.  I'd say to be comfortable, you'd probably want to see more like 1400-1500.

All you have to remember is that the Heroics are generally about a half-step behind Karazhan in terms of gear requirements and rewards, so if you can run one, chances are you can run the other.

I agree with IZBadAzz, it is not a black and white issue.

SlavePens, Underbog, Ramparts, etc. are easy Heroic instances. But even with 1400 Healing Bonus you could struggle if your group is not properly balanced.

As a Holy Priest with 1300 HB, I went into Ramparts with a druid who had nearly 15K health (in bear form) and I hardly had to do much . He would hold aggro like a dream, the DPS people kept pumping damage steadily, while the Rogue complemented the Druid tanking.  It was also good practice to master the 5 Second Rule.

Same instance, two days later, our Prot Warrior only had 11k health. I kept running out of mana, since he kept getting low on health. The 5SR went out of the window. The DPS also didn't have Omen, and he took the aggro too many times. Result: a disaster.

So, a few rules for you (regarding Heroics):

• 1200 Healing Bonus I would say is a minimum.
  
• Have a balanced party: have a good tank with 13k+ health, two DPS (Mage, Warlock), and a Rogue or a Hunter.
  
• Have a sizable mana pool yourself.
  
• Try to use the 5SR when possible.
  
• Gear up properly: PvP gear is ok for a start, but it is not the best for the big PvE instances. Try to get the new stuff as soon as you can. Spirit and Intellect seem to be the best stats to build up nowadays.
  
• I would also advise to do test runs with guildies if you can: Practice different combinations/strategies with the first few mobs in the instance.
  

I'm sure some people may have other opinions, so feel free to amend/add as required :-)

ty alot for  the advice, it really helped:D